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97 lines
3.4 KiB
97 lines
3.4 KiB
9 years ago
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/* ----------------------------------------------------------------------
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* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
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*
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* $Date: 12. March 2014
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* $Revision: V1.4.4
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*
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* Project: CMSIS DSP Library
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* Title: arm_cos_q15.c
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*
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* Description: Fast cosine calculation for Q15 values.
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*
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* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* - Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* - Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* - Neither the name of ARM LIMITED nor the names of its contributors
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* may be used to endorse or promote products derived from this
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* software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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* -------------------------------------------------------------------- */
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#include "arm_math.h"
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#include "arm_common_tables.h"
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/**
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* @ingroup groupFastMath
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*/
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/**
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* @addtogroup cos
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* @{
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*/
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/**
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* @brief Fast approximation to the trigonometric cosine function for Q15 data.
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* @param[in] x Scaled input value in radians.
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* @return cos(x).
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*
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* The Q15 input value is in the range [0 +0.9999] and is mapped to a radian
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* value in the range [0 2*pi).
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*/
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q15_t arm_cos_q15(
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q15_t x)
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{
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q15_t sinVal; /* Temporary variables for input, output */
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int32_t index; /* Index variables */
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q15_t a, b; /* Four nearest output values */
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q15_t fract; /* Temporary values for fractional values */
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/* add 0.25 (pi/2) to read sine table */
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x += 0x2000;
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if(x < 0)
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{ /* convert negative numbers to corresponding positive ones */
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x = x + 0x8000;
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}
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/* Calculate the nearest index */
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index = (uint32_t)x >> FAST_MATH_Q15_SHIFT;
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/* Calculation of fractional value */
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fract = (x - (index << FAST_MATH_Q15_SHIFT)) << 9;
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/* Read two nearest values of input value from the sin table */
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a = sinTable_q15[index];
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b = sinTable_q15[index+1];
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/* Linear interpolation process */
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sinVal = (q31_t)(0x8000-fract)*a >> 16;
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sinVal = (q15_t)((((q31_t)sinVal << 16) + ((q31_t)fract*b)) >> 16);
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return sinVal << 1;
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}
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/**
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* @} end of cos group
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*/
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